The present invention relates to detecting fraud in the use of an electronic circuit card. A particularly advantageous application of the invention lies in combating fraud concerning calls made from a telephone, particularly but not exclusively a public pay phone.
The cards used in pay phones, also known as phone cards, are generally xe2x80x9csynchronousxe2x80x9d electronic circuit cards which produce an output signal that is a function based on combinatory or sequential logic applied to a combination or a sequence of one or more input signals. Before becoming operational, synchronous circuits require a powering-up time of about 500 ns, for example.
The popularization of electronic circuit card technology by large circulation electronics magazines and also in technical training establishments has contributed greatly to attempts at making fraudulent use of telephones by emulating electronic circuit cards, i.e. phone cards designed to operate with such telephones. In addition, the widespread availability of sophisticated components such as programmable microprocessors, and the ease with which they can be used based on knowledge acquired in school laboratories or from programmers of microprocessors, make it likely that this type of fraud will increase.
In particular, programmed logic phone card simulators are available known as xe2x80x9cactivexe2x80x9d simulators. These are asynchronous electronic circuit devices essentially comprising a programmable microcontroller associated with a few passive components (resistors, capacitors). By means of an internal program, the microcontroller simulates the behavior of a phone card. Components of this type are now widely available on the consumer market, as are development and programming tools therefor, in particular software that runs on personal computers.
In general, phone card fraud involves connecting the active simulator to the electrical contact zones of the electronic circuit of the phone card by means of connection wires so as to connect the simulator to the electronics of the telephone. In order to detect this type of fraud, it is possible to fit the telephone with a specific device known as an external connection detector (ECD). This detector device is mainly constituted by a large and plane electrode suitable for overlaying the connection wires connecting the simulator to the contact zones. In the absence of fraudulent connection wires, the only electrical capacitance present between the card and said electrode is a capacitance C0 due to the environment of the card and of the electronics. However, the presence of fraudulent connection wires creates a distributed capacitance C1 between the plane electrode and the contacts of the pay phone terminal. The principle on which an ECD operates is thus to detect the increase of capacitance from C0 to C0+C1 when a phone card is inserted that has had connection wires to a simulator fitted thereto.
Detection by means of an ECD suffers from the drawback of the parasitic capacitance C1 drifting as a function of temperature and humidity. Therefore, in order to obtain best performance in terms of the number of wires that can be detected, it is necessary to provide automatic correction in hardware, or semiautomatic correction in software. It is then advantageous to make use of a differential circuit for canceling the effects of such drift in the parasitic capacitance.
One object of the present invention is to provide an improved technique for detecting fraud in use of a phone card.
A more specific object of the present invention is to detect fraud in use of a phone card which is conducted with an active phone card simulator without having to provide a correction for drifting of a parasitic capacitance.
This and other objects are attained in accordance with one aspect of the present invention directed to detecting the fraud that involves using an asynchronous circuit in the place of a card having an electronic circuit that is synchronous, presenting a given power-up time. A given excitation signal is applied to the electronic circuit of the card upon power-up, a response pattern outputted by the circuit is recorded, the response pattern is compared with a reference pattern corresponding to the response expected from the electronic circuit to such excitation signal, and the fraudulent use is identified by means of an asynchronous circuit when the comparison is negative.
As explained in greater detail below, the invention makes it possible to detect the fraudulent presence of an active phone card simulator by making use of the fact that an asynchronous electronic circuit can simulate a phone card only after a certain amount of time has elapsed after the circuit has been powered. This minimum length of time is never shorter than 10 ms. When a card, whether an authentic card or an active type fraudulent card, is inserted into the reader of a pay phone for example, a power supply voltage is delivered to the card by the reader. It will thus be understood that if a given excitation signal is applied to the input of the circuit of the card present in the reader after a length of time that is equal to or slightly greater than the power-up time required to enable a synchronous circuit to operate, then the response pattern supplied by the circuit will be the expected reference pattern if the card is authentic, whereas if the card is a fraudulent card having an asynchronous circuit, then the response pattern will be completely erratic since the circuit is not yet ready to operate, thus enabling fraud to be diagnosed.